1. Fields of the Invention
One aspect of the present invention relates to the formation of a stable colloidal dispersion of fine particles. More particularly, the invention relates to the formation of nanocomposites.
Another aspect of the present invention further relates to the formation of continuous films of submicron particles.
A further aspect of the present invention relates to a ferrofluid having low optical density. Further, the invention relates to a method of preparing the ferrofluid. More particularly, the invention relates to a method of preparing an aqueous ferrofluid. More specifically, the invention relates to a method for the preparation of colored ferrofluids using various colorants, dyes or pigments.
Still another aspect of the present invention relates to the direct preparation of premicronized low optical density magnetic material from submicron ion exchange resin.
A further aspect of the present invention further relates to magnetic materials having tunable magnetic properties, and more specifically, the present invention relates to magnetic materials containing both single-domain and multidomain particles. More particularly, the present invention relates to magnetic materials having high initial permeability while maintaining coercivity and remanence in the pigment.
Another aspect of the present invention relates to a method for making low optical density magnetic fluids containing both single-domain and multidomain particles. More specifically, the invention relates to a method for the preparation of colored magnetic particles and ferrofluids using various colorants, dyes or pigments.
A further aspect of the invention relates to xerographic magnetic liquid toners, colored xerographic magnetic liquid toners and liquid ink compositions and methods of preparation thereof.
Still a further aspect of the invention relates to liquid developers and methods of making the same.
Another aspect of the invention further relates to ink jet applications and more specifically, ink jet inks and methods of making and use the same.
Still another aspect of the invention relates to the preparation of dry particles or fluid materials produced by fluidization and micronization of a material and the subsequent drying thereof to yield dry particles which may be used in a dry state or redispersed in a fluid medium.
Still another aspect of the invention relates to the preparation of materials using resins with a plurality of functional groups to allow precipitation which maintaining binding sites.
Finally, one aspect of the invention relates to the preparation of an MICR composition and a method of making and using that composition.
2. Discussion of the Prior Art
Prior art formation of submicron or nanometer structures have predominantly included the formation of large particles which are subsequently ground or milled until particles of the desired size are achieved. The grinding and milling times associated with the formation of such particles ranged from 120 to 2900 hours.
A method of forming dry magnetic submicron particles by precipitation of a magnetic oxide in an ion exchange resin is discussed and exemplified by Ziolo in U.S. Pat. No. 4,474,866, which is incorporated herein by reference. According to the method employed, an ion exchange resin is loaded with a magnetic ion. The resin is then recovered and dried. The magnetic polymer resin is then micronized to form a fine magnetic powder. The dry magnetic particles formed according to Ziolo, U.S. Pat. No. 4,474,866, like other typical prior art materials, could not be directly suspended in an aqueous medium to form a stable colloid.
Difficulties have been encountered in forming and maintaining nanoscale materials due to the tendency of the particles to aggregate to reduce the energy associated with the high area to volume ratio. This aggregation leads to additional difficulties in the preparation of homogeneous dispersions and thin continuous films produced therefrom.
Prior art formation of films of submicron particles have required the spreading of fine particles which resulted in uneven and noncontinuous films. In addition, if the particles were dispersed in a fluid medium, upon evaporation of the fluid medium, film properties were not continuous but were individual islands of particulate material. By contrast, the fluids of the present material are a composite of a crushed matrix material and nanometer particles in an aqueous vehicle. Upon evaporation of the aqueous vehicle in the present invention, the particles are left in a continuous film joined by a network of this crushed resin material.
More specifically, the preparation of magnetic fluids is, in general, a very time intensive process most simply done by grinding a magnetic material such as magnetite, Fe.sub.3 O.sub.4, in a suitable liquid vehicle in the presence of a dispersing agent or surfactant to obtain a stable colloidal magnetic fluid. This general preparation is described in detail in Rosensweig & Kaiser "Study of Paramagnetic Liquids," NASA Document N68-14205, Wilmington, Mass. 1967 and IEEE Transactions on Magnetics, Vol. MAG-16, No. 2, March 1980, which is incorporated herein by reference.
In a typical grinding or milling operation to produce magnetic fluids, grinding or milling times of 120-2900 hours (five days to four months) are required. The problem is in producing small enough magnetic particles to enable the formation of a stable colloid. The use of dispersing agents or surfactants is also a problem in that the correct or enabling surfactant must be found empirically. Furthermore, the surfactant may degrade or cause adverse chemical reactions in the magnetic fluid during its application.
In addition, prior art magnetic fluids are typically, by their very nature, black or very dark brown in color and therefore highly absorbent in the visible region of the spectrum. At the heart of such materials are magnetic materials such as iron, cobalt or nickel particles, iron oxide such as Fe.sub.3 O.sub.4, and the like, generally in an assigned range of about 10-1000 .ANG.. These prior art magnetic fluids are not particularly useful in applications requiring low optical density as they are highly absorbing. Examples of such applications include those requiring high magnetism and low optical density or high optical transmission, particularly in the visible and near infrared region of the spectrum, such as, magneto-optic and electro-optic effects.
Moreover, if a fluid with these magnetic properties is required to be colored, i.e. by mixing it with various colorants, dyes or pigments, the brown, black or muddy appearance of the prior art magnetic fluids produced a colored magnetic fluid which was also brown, black or muddy in appearance. Thus, applications requiring brightly colored fluids that are magnetic, for example, inks and toners were not possible using the prior art magnetic fluids. Moreover, when colorant was added to prior art magnetic fluids, a mixture of dye and magnetic fluid was formed. If a single component colored fluid was required, its formation was not possible using prior art magnetic fluids.
In standard one and two component xerographic and other magnetic imaging systems, the magnetic pigment used has both a remanence and coercivity that enables the pigment to function in the applied field. Due to the remanence and coercivity properties of the magnetic pigment, prior art materials required high weight or volume loading of the pigment in order to get an initial permeability high enough to make the material useful.
Magnetic pigments having high initial permeability are desirable because they allow for substantially lower pigment loadings which in turn improves the rheological properties of a toner or developer or improves the optical properties of, for example, a single component highlight color or color clean machine subsystem.
Prior art superparamagnetic (SPM) materials for use as magnetic pigments provide the desired high initial permeability. These materials are not entirely satisfactory as they have no coercivity or remanence which are necessary for certain applications, i.e. any application requiring a memory. Such superparamagnetic materials have no memory in that, they are only magnetic in the presence of a field and have no net magnetism outside the field.
Ferrofluids which contain superparamagnetic materials as described above, are recognized within the prior art for a number of applications, including exclusion seals for computer disc drives, seals for bearings, for pressure and vacuum sealing devices, for heat transfer and damping fluids in audio speaker devices and in inertia damping. Tyrpical prior art superparamagnetic materials such as those described by Wyman in U.S. Pat. No. 4,855,079, which is incorporated herein by reference, are coated particles which are in an organic based carrier material. More specifically, this patent discloses a superparamagnetic material which is formed by the precipitation of the magnetic particles (magnetite). These particles were subsequently coated with an oleic acid surfactant. The coated particles were eventually suspended in an organic dispersing agent. Again, the use of dispersing agents or surfactants is a problem in that the right or enabling surfactant must be found empirically, and the surfactant may degrade or cause adverse chemical reactions in the magnetic fluid during its application.
A method of forming dry magnetic particles by precipitation of a magnetic oxide in an ion exchange resin is discussed and exemplified by Ziolo in U.S. Pat. No. 4,474,866, which is incorporated herein by reference. According to the method employed, an ion exchange resin is loaded with a magnetic ion. The resin is then recovered and dried. The loaded resin does not contain single-domain and multidomain crystallites internal and external to the resin bead, respectively. The magnetic polymer resin must then be micronized to form a fine magnetic powder. The micronization step is a time and energy intensive process. The dry magnetic particles formed according to Ziolo, U.S. Pat. No. 4,474,866, like other typical prior art materials, could not be directly suspended in an aqueous medium to form a stable colloid.
None of the heretofor known prior art magnetic materials contain both single-domain and multidomain crystallites. Domain as used herein is described for example in C. P. Bean and J. D. Livingston, J. Appl. Physics 30, 120s (1959) and B. D. Cullity, Introduction to Magnetic Materials, Addison-Wesley Publishing Co., MA, (1972), both of which are incorporated herein by reference.
The presence of both single-domain and multidomain crystallites provides the ability to tune the magnetic properties to match the desired use for the material. By varying the amount of single-domain and multidomain crystallites with respect to one another it is possible to provide a material whereby the properties of high initial permeability, remanence and coercivity may be varied relative to one another.